Caption: Streptococcus salivarius. Transmission Electron Micrograph (TEM) of a chain of Streptococcus salivarius bacterial cells. The chain is bound together by the capsular material seen around each cell. S. salivarius is a Gram-positive, non- motile, spherical bacterium which forms part of the permanent bacterial population of the human mouth. Immune responses from the host, in the form of antibody attack, are repelled by the bacteria's ability to alter it's surface proteins and thus remain "unidentified" by antibodies. Certain strains of S. salivarius can contribute to tooth decay. Magnification: x 165,000 at 8x10 inch size.